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Abstract

We propose a novel photon number resolving detector structure with large dynamic range. It consists of the series connection of N superconducting nanowires, each connected in parallel to an integrated resistor. Photon absorption in a wire switches its current to the parallel resistor producing a voltage pulse and the sum of these voltages is measured at the output. The combination of this structure and a high input impedance preamplifier result in linear, high fidelity, and fast photon detection in the range from one to several tens of photons.

Figures (8)

Electrical circuit and layout schematics for the implementation of SND structures. The voltage source in series with a bias resistor provides the biasing of the detector through the DC arm of the bias-T. The RF arm is connected to the amplifier circuit. N nanowires, each with a resistor in parallel, are connected in series. The voltages produced by photon absorption in different sections are summed up in the output.

Transient current flowing through the (a) firing, If and (b) unfiring, Iuf section of an SND with N = 10, RL = 50Ω, Ib = 0.99Ic, Rp = 80Ω after absorption of n = 1-10 photons. (c) Corresponding output voltage Vout. Transient current (d) If and (e) Iuf with the ideal 1MΩ load readout, which are independent of the number of absorbed photons. The large load impedance decouples firing and unfiring sections. (f) The related output voltage with RL = 1MΩ. The dashed lines are exponential fits to the rise/fall times, as explained in section 6.

Transient response of an SND with N = 100, Ib = 0.99Ic, Rp = 80Ω, and RL = 1MΩ. (a) Current flowing through the firing If, and unfiring Iuf, sections, the parallel resistor IRp, and the load Iout. (b) Output voltage of the SND when n = 1,2,3 photons are absorbed. (c) Peak output voltages as a function of the number of absorbed photons together with a power-law fit (solid lines) plotted in log-log scale as Vout = Anα. For the case of the high impedance load (1MΩ), α = 1 both for N = 10 and N = 100, (red squares and blue circles, respectively). The response is very close to linear (α = 0.9) even with the 50Ω load (green triangles).

Equivalent circuits used to extract the time constants corresponding to the (a) inductances of the firing branches, (b) inductances of the unfiring branches, and (c) the total inductance after the wires have switched back to the superconducting state. (d), (e) The calculated time constants of the N = 10 elements SND with RL = 50Ω and RL = 1MΩ, respectively. Increasing RL improves the response time dramatically, without causing latching.

Output voltage of an SND with N series section each connected in parallel to Rp = 40Ω and biased at Ib = 0.99Ic, considering the effect of C = 180fF input capacitor in parallel to the load resistor. (a) N = 10, and RL = 10kΩ when n = 1,2,…,10 photons are detected. The inset shows the linearity of the peak output voltages as a function of the number of detected photons together with a power-law fit (solid line) plotted in log-log scale as Vout = Anα where α = 0.96 (b) N = 100, and RL = 1MΩ. The inset shows the power-law fit of n = 1-100 detected photons with excellent linearity of α = 0.99.

(a) Probability of detecting n = 1-10 photons when n = 1-10photons hit the SND with N = 100 detecting elements, with different values of QE = 0.8, 0.9, and 1. (b) Calculated average number of detected photons <ndet> as a function of the average number of incident photons <ninc>, evenly distributed to N = 100 detecting sections of the SND with unity QE (blue circles), compared with ideal response, the light blue line with slope = 1.